Recent panel display devices are often configured to be adapted to touch sensing, which involves sensing a contact of an object such as human fingers onto the display panel. A display panel adapted to touch sensing can be used as an input-output device by itself and this effectively improves user-friendliness. The “touch sensing” referred to herein includes sensing the position at which an object is placed into contact with the display panel, and may further include detecting the contact pressure.
A panel display device, especially when used in a portable terminal, is often designed to reduce the volume thereof. To fulfill this expectation, techniques using common electrodes, which are connected only to capacitive loads, as sense electrodes for touch sensing have been proposed with respect to liquid crystal display panels. It should be noted that the common electrodes are often referred to as counter electrodes instead. Use of common electrodes as sense electrodes for touch sensing allows achieving touch sensing without provision of a touch panel separately from the liquid crystal display panel.
In contrast, a display panel which uses current-driven elements in the respective pixel circuits, such as OLED (organic light emitting diode) display panels, is not adapted to touch sensing through this approach, because this type of display panel does not include common electrodes connected only to capacitive loads. One alternative approach is to additionally incorporate sensing elements for touch sensing within a current-driven display panel such as OLED display panels.
A current-driven display panel is designed to reduce the numbers of circuit elements, such as thin film transistors. The reduction of the number of additional circuit elements and routing traces contributes facilitation of design and manufacture process. There is a technical need for reduction of the number of circuit and routing traces elements additionally incorporated to achieve touch sensing.
U.S. Pat. No. 8,427,435 and Takahashi et al. “Embedded Liquid Crystal Capacitive Touch Screen Technology for Large Size LCD applications”, SID Symposium Digest, pp. 563-566, 2009 disclose techniques for integrating touch sensors including sensor capacitors in a liquid crystal display panel.
Park et al. “High-Speed AMOLED Pixel Circuit and Driving Scheme”, SID Symposium Digest, pp. 806-809 discloses configurations of pixel circuits of OLED display panels, more particularly, a 6T1C-type pixel circuit and a 5T1C-type pixel circuit.